1. The Field of the Invention
The present invention relates to a safety device used particularly in motor vehicles, which upon the onset of a collision, deploys an inflatable restraint cushion, known as an air bag cushion, to protect the occupants of the vehicle from the impact of the collision. More particularly this invention relates to an air bag inflator which uses percussion primers as part of the ignition assembly.
2. The Relevant Technology
An air bag safety system is typically activated after receiving a signal from a detector or sensor that indicates that inflation of the air bag cushion is required. Various types of inflators are used in air bag safety systems to rapidly deploy the air bag cushion. One type of inflator, shown generally in FIG. 1 as reference number 10, utilizes an activating assembly 12 which initiates inflation of the air bag assembly by triggering an electroexplosive device 14 to "remove" a barrier 16 disposed between activating assembly 12 and an inflating medium contained within the inflator housing 18. Upon barrier 16 being removed, the inflating medium contained in inflator housing 18 is supplied to the air bag cushion (not shown) of the air bag safety assembly. The inflating medium can be pressurized gases, gases generated by combustion of a gas generating material or propellent, a mixture thereof, or other suitable fluids.
Barrier 16 is typically removed by breaking or penetrating barrier 16 using an object that is directed at barrier 16 upon triggering electroexplosive device 14 within activating assembly 12. Many types of objects have been used to "remove" barrier 14. One method of removing barrier 16 utilizes activating assembly 12 that includes a projectile 20. Once electroexplosive device 14 in activating assembly 12 is triggered, projectile 20 is propelled towards barrier 16. In some inflators once projectile 20 pierces barrier 16, pressurized gas contained within inflator housing 18 fills the air bag cushion (not shown). In other inflators, such as inflator 10, when projectile 20 pierces barrier 16 the pressurized gas contained within inflator housing 18 begins to fill the air bag cushion. Simultaneously, projectile 20 continues its flight until it strikes igniting assembly 22 which ignites gas generating material 24. Gas generating material 24 rapidly generates gas to complete inflating the air bag cushion.
In this type of inflator 10, generally speaking, projectile 20 is released upon triggering activating assembly 12 to ignite a percussion primer 26 in igniting assembly 22. More specifically, projectile 20 strikes an actuating member, such as an actuator plate 22, that is part of igniting assembly 22. The impact of projectile 20 causes actuator plate 22 to be displaced to strike percussion primer 26 and ignite gas generating material 24. Current designs and technology of available inflators have several problems that adversely effect the performance of the inflator.
A first problem is that this type of an inflator has numerous components that make the inflator expensive to manufacture and assemble. A less costly inflator would include fewer and/or simpler parts. Merely using inexpensive parts, such as a less expensive actuator plate, however, does not solve the problem and actually exasperates the more significant problems with current designs of an inflator, such as inflator 10, illustrated in FIG. 1.
One problem that is experienced with current designs of inflators, such as inflator 10, is that pressurized gas contained in inflator housing 18 gets into igniting assembly 28 and becomes trapped, particularly in the space under actuator plate 30. The trapped pressurized gas causes actuator plate 30 to move toward projectile 20 and barrier 116. This is particularly problematic when a thinner, more flexible, or less expensive actuator plate 30 is used in igniting assembly 28. This phenomena is often referred to as "bulging".
When actuator plate 30 is impacted by projectile 20, actuator plate 30 moves longitudinally away from barrier 16 and impacts percussion primer 26. The movement of actuator plate 30 to impact primer 26 is referred to as the "actuating stroke." When actuator plate 30 is bulging, the actuating stroke performed by actuator plate 30 has an insufficient depth. Any bulging of actuator plate 30 causes the actuating stoke of actuator plate 30 to either miss primer 26 or to fail to strike primer 26 sufficiently hard to ignite gas generating material 24. Consequently, both performance and reliability of the entire air bag safety system has been damaged and sacrificed.
Further, in the current designs of ignitor 10, actuator plate 30 fails to prevent the gases being rapidly formed by gas generating material 24 from passing around the edges of actuator plate 30 instead of exiting in the predetermined direction. Bulging may also occur in those instances when percussion primer 26 has a hole in it or is even missing allowing even more compressed gas to be trapped under actuator plate 30. Any bulging of actuator plate 30 pulls the edge of actuator plate 30 away from the interior surface of gas generator housing 28. Consequently, current designs of inflators 10 and particularly, actuator plate 30 do not maintain a seal with gas generator housing 28. When actuator plate 30 bulges under the force of either the pressurized gas or the gas being rapidly generated, there is a gap between the interior surface of gas generator housing 28 and the edge of actuator plate 30 through which the gas flows around actuator plate 30 toward activating assembly 12. This "back flow" of gases around actuator plate 30 is detrimental to the air bag safety system as well as hurting the overall performance of inflator 10 because if allowed, the hot gases being rapidly generated by gas generating material 24 will flow directly into the air bag cushion (not shown) and can scorch or burn the air bag cushion. There is the real potential that the back flow of hot gases around the edge of actuating plate 22 will actually burn a hole through the air bag cushion.
Accordingly, there is a need to improve the igniting assembly of inflators that use percussion primers in the igniting assembly to overcome the foregoing disadvantages. In addition, there in a need to improve the inflators such that the inflator itself is comprised of fewer, simpler parts, thereby making the inflator less costly to manufacture and assemble without sacrificing accuracy or reliability.